If there has been anyone similar to Snake then I'm confident it hasn't been released information. There was one situation with George A. Koval who remained uncaught for many years and was the only one (that we know of) to have top-level security clearance in the US. He was the "only Soviet intelligence officer to penetrate the U.S. secret atomic facilities producing the plutonium, enriched uranium and polonium used to create the atomic bomb."

He was born in the Sioux City, Iowa, USA and his parents were from Belarus. They immigrated to the US after the Soviet Union merged. He studied electrical engineering at the University of Iowa, but after the Great Depression he moved to the Soviet Union in 1932. He attended college at Mendeleev Institute of Chemical Technology and graduated in 1939 and gained a Soviet Citizenship.

He was a grade A student and caught attention of Soviet Union’s Main Intelligence Directorate (Гла́вное разве́дывательное управле́ние), or using Roman letters: Glavnoye Razvedyvatel'noye Upravleniye (GRU).

Since he was born in the US, he already had a citizenship that was easy to get him back in. They sent him to the US using the name Delmar and he landed in San Francisco and moved to New York. By this time it's 1941 and he was drafted into the US Army.

Through a fake degree of Associate Degree in Chemistry from a community college in New York, he was selected to join the Army Specialized Training Program and studied electrical engineering with some other top candidates. These candidates were asked to join Special Engineer Detachment, who became part of The Manhattan Project.

Throughout this time he sent recipes and various locations to the GRU until 1946 when he was honorably discharged from the Army after refusing a promotion due to (later revealed) worry about tighter security. In 1948, he told his friends he was going to travel to Europe. He went back to The Soviet Union and never returned back to the US.

Source

Any explanation of all the deleted threads?

NOTE: Originally posted, erroneously, to a different question. Welcome home, Mucius.

According to Livy's Ab Urbe Condita, a quasi-historical account of the earliest days of Rome, Gaius Mucius Scaevola ended an Etruscan siege of Rome that threatened to destroy the city by sneaking into the Etruscan camp at night (with the Senate's approval) in an attempt to assassinate the Etruscan king Lars Porsenna. Unfortunately, he misidentified one of Porsenna's well-dressed scribes as the king and killed him instead. He was captured and taken before Porsenna. After giving a threatening oration to the king and the assembled Etruscans in which he stated that the youths of Rome would be coming for the king's head until the war was over, Porsena ordered him thrown into the flames. Before his guards could do so, however, Mucius announced:

Look, that you may see how cheap they hold their bodies whose eyes are fixed upon renown!

Whereupon he thrust his own right hand into a nearby sacrificial fire until it burnt to a crisp, without showing any pain. Porsenna was so impressed with Mucius and fearful of the courage of the Romans that he set Mucius free and sent ambassadors to Rome immediately to negotiate peace. From then on, Gaius Mucius was given the cognomen Scaevola, meaning "left-handed," a name that was passed down to his progeny.

Now, this being Livy, it may or may not be "strictly historical." But it's a good story, and if nothing else it tells us about how aristocratic Imperial Romans thought about their past.

Well, considering that in Metal Gear Solid 3, and in the beginning of MGS4 Act 2 Snake does a lot of slow crawling motions through bushes where he appears to move like a worm, here's a very similar example.

In Vietnam Carlos Hathcock had stalked a North Vietnamese Army general, probably his most high-value target ever, for two days and three nights. During his stalk, Hathcock moved only inches at a time, covered bare yards in an hour. Enemy patrols had been moving all about him as he stalked his quarry, one soldier even brushing against his leg as he walked by, but never noticing the sniper in the tall grass. The distance Hathcock covered during his stalk was only two thousand meters of flat ground covered with two-foot-tall grass. He made his shot from eight hundred meters and withdrew while a furious enemy force scoured the area for him.

Source: http://books.google.com/books?id=nYWZFOKFQ2gC&pg=PT156

I'm late to the party but I do know of one in World War II: Captain Witold Pilecki of Polish Home Army. He infiltrated Auschwitz-Birkenau as a prisoner in order to figure out what was going on in them, organized a small resistance and busted out, taking out a guard and communication lines in the process.

Here is a copy of his findings.